Self-deploying drag reducing device

ABSTRACT

A drag reducing apparatus is hingedly mounted to the rear of a truck or trailer vehicle so that the apparatus can be pivoted clear of the rear doors of the vehicle. The apparatus includes a hinge assembly that allows the apparatus to open substantially flat against the side of the vehicle so as not to impede the full movement of the doors. The apparatus includes an arrangement of connected panels that are initially folded flat against the back of the vehicle but automatically open to a drag reducing configuration at a sufficient vehicle speed. The connected panels are further configured so that the force of gravity automatically returns the panels to their initial folded configuration when the vehicle speed falls below a threshold. The apparatus incorporates a modular construction that allows replacement of individual panel sections. The mounting frame is constructed to augment the drag reduction characteristics of the apparatus.

CLAIM OF PRIORITY

This application claims priority to application Ser. No. 12/368,614,filed on Feb. 10, 2009 and issued on Dec. 21, 2010 as U.S. Pat. No.7,854,468, which claims priority to provisional application No.61/065,490, filed on Feb. 12, 2008, the entire disclosures of which areincorporated herein by reference.

BACKGROUND

The present disclosure relates to drag reduction devices for landvehicles, such as trucks, tractor-trailer rigs, vans, buses,recreational vehicles and similar vehicles having a large frontal area.

Fuel economy is a persistent concern for all land vehicles and isparticularly acute for large vehicles such as trucks and tractor-trailerrigs. Fuel economy improvements have been achieved by innovation inengine design and improvements in fuel composition. However, the sizeand shape of the vehicles plays a substantial role in fuel economy.Ultimately, drag is the greatest enemy to fuel economy, with as much as70% of the engine power devoted to cutting through the air in front ofthe vehicle.

Drag is a force that resists the movement of a body through a fluid,whether the body is a baseball and the fluid is air, or the body is aswimmer moving through water. Drag is a function of twocomponents—friction drag and pressure drag. Friction drag is a forcethat acts tangential to a surface of the body. Friction drag isincreased by irregularities or roughness on the surface and decreased bymaking the surface more slippery. A clean truck cuts through the airmore efficiently and with less friction drag than a dirty truck.

Pressure drag is a force that acts perpendicular to a surface and is afunction of the surface area in the direction of travel as well as thevelocity or speed at which the body is traveling. Pressure dragincreases as the square of velocity so that doubling vehicle speedactually creates four times more pressure drag. On the other hand,pressure drag is directly related to surface area so that a ten percentreduction in surface area leads to a ten percent decrease in pressuredrag.

For aerodynamically configured vehicles, such as airplanes, frictiondrag contributes more heavily to overall drag than pressure drag.However, for land vehicles this relationship is reversed significantly.For a typical tractor-trailer, pressure drag can be as much as ten timesgreater than friction drag due to the large frontal surface area of thetruck. Unfortunately, the size of these types of vehicles is dictated bytheir function—hauling products or materials. Unlike passenger vehicles,the box-like shape of trucks cannot be significantly altered. A smallerfrontal surface area means a smaller truck, which means less cargo thatcan be hauled. Pressure drag in land vehicles, and especially in trucks,is increased by pressure “hot spots”, such beneath the undercarriage,behind the rear of the trailer or between the tractor and the trailer.These hot spots are generally regions of low pressure, which causes airflowing over the vehicle to deviate from a streamlined path around thevehicle. Vortices can form in these hot spots that significantlyincrease the pressure drag.

In quantitative terms, if a square body has a drag coefficient (C_(D))of 1.00, elongating the body into a rectangular shape reduces C_(D) to0.80. Adding a rounded nose cuts the coefficient in half to 0.40. Addinga “boat tail” or a conical tail decreases C_(D) further to 0.20. Anelliptical body tapered at both ends produces a drag coefficient lessthan 0.05, but the shape significantly reduces available cargo space andis difficult to produce.

It has been estimated that a 20% reduction in drag yields at least a 10%increase in fuel economy at highway speeds. For truckers and truckingcompanies, this increase in fuel economy means significantly reducedfuel costs year in and year out. For the environment, increases in fueleconomy mean fewer deleterious emissions. A significant amount of efforthas been expended in developing drag reduction technology for trucks.These efforts include streamlining the tractor, introducing seals, airdeflectors or vortex generators in the gap between the tractor andtrailer, and adding undercarriage skirts, guide vanes, air deflectorsand boat tails to the trailer. Each of these modifications contributesin some measure to the overall drag reduction, so a fully optimized rigwill incorporate a number of these improvements.

One of the greatest contributors to drag reduction is the boat tail orboat tail plates extending from the rear of the trailer. A boat tailreduces drag by about five percent. The typical boat tail is a largeshell that is mounted over the rear doors of the trailer. Such devicesare cumbersome to install and remove. Moreover, the large unitary shellis difficult to store when access to the rear doors is desired, such asto unload the trailer. An improved drag reducing device will provide thesame aerodynamic benefits as the traditional boat tail without theundesirable attributes.

SUMMARY

In one embodiment, a drag reducing apparatus for a vehicle comprises anupper panel section, a lower panel section and opposite side panelsections, each of the panel sections hingedly mountable around aperimeter of the rear of the vehicle. The upper panel section ishingedly connected to an upper end of each of the side panel sectionswhile the lower panel section is hingedly connected to a lower end ofeach of the side panel sections. The panel sections have a folded statein which each panel section is substantially flat against the frame withthe side panel sections overlying the lower panel section and the upperpanel section overlying the side panel sections. In one aspect, thehinged connections between panel sections are configured so that thepanel sections automatically move from the folded state to an extendedstate at an airflow around the rear of the vehicle sufficient to pivotat least the upper panel section upward from the folded state. As theupper panel pivots upward, it pulls the side panel sections outward,which in turn pull the lower panel section outward to an aerodynamicdrag-reducing shape.

In a further aspect, the drag reducing apparatus further comprises aframe having a perimeter and opposite side sections, in which the panelsections are hingedly connected to the perimeter of the frame. A hingearrangement, attachable to the rear of the vehicle, is provided at oneof the side sections of the frame. A latch arrangement is provided atthe other side section of the frame, and is configured to releasablylock the frame to the rear of the vehicle. The hinge arrangement allowsthe entire drag reducing apparatus to be pivoted out of the way of therear of the vehicle to permit access, for example, to loading doors ofthe vehicle.

In another aspect, the frame, the upper panel section and the lowerpanel section include a center hinge arrangement configured to permitone of said side sections of the frame to be pivoted about the centerhinge arrangement onto the other side section when the panel sectionsare in the folded state. This feature allows only one side of theapparatus to be moved clear of one side of the rear of the vehicle, suchas to access a single door. In addition, this feature, combined with thehinged attachment, allows the entire apparatus to be folded in half andthen pivoted clear of the rear of the vehicle.

In a further embodiment, a drag reducing apparatus for a vehicle havinga pair of opposing rear doors hinged from the sides of the vehicle,comprises a frame having a perimeter and connectable to the rear of thevehicle and offset therefrom to accommodate the rear door hinges, anupper panel section, a lower panel section and opposite side panelsections. Each of the panel sections is hingedly connected around theperimeter of the frame, while the upper panel section is hingedlyconnected to an upper end of each of the side panel sections and thelower panel section is hingedly connected to a lower end of each of theside panel sections. The hinged connections between panel sections isconfigured so that pivoting one of the panel sections about a hingedconnection automatically moves all of the panel sections from a foldedstate in which the panel sections are substantially flat against theframe to an extended state in which the panel sections project outwardfrom the perimeter. The apparatus further includes a series of platesattached to the frame around the perimeter and disposed between thepanel sections in the folded state and the rear of the vehicle. Theseinboard panels help offset or cancel the drag effects caused by theoffset or gap between the apparatus and the rear of the vehicle.

In another feature, the hinged connection between each of the panelsections and the perimeter of the frame includes a sliding interlockinginterface. In one embodiment, this interface includes a rib in slidinginterlocking engagement with a slotted beam forming the perimeter of theframe. This sliding interlocking interface simplifies construction andallows a given panel section to be removed and replaced.

Another aspect of certain embodiments of the drag reducing apparatusresides in the hinged connections between panel sections including aremovable fastener strip. This fastener strip permits removablyconnecting adjacent panel section together, which simplifies assemblyand facilitates removal and replacement of a particular panel section.

In yet another feature, the drag reducing apparatus includes tethersheets connected between the free edge of the panel sections and theapparatus frame. The tether sheets fold with the panel sections in thefolded state. When the panel sections move to the extended state, thepanel sections extend at an angle from the free edge of the panelsection to the apparatus frame. In certain embodiments, the tethersheets at the upper and side panel sections are formed of a meshmaterial, while the tether sheet for the lower panel section issubstantially solid for rain and snow run-off.

One benefit of the drag reducing apparatus disclosed herein is that itmay be self-deployed and automatically deployed or undeployed based onthe speed of the vehicle. Air pressure at the rear of the vehicle movesthe apparatus to its deployed state, while gravity operates to returnthe apparatus to its undeployed state. As needed, the apparatus may alsobe easily deployed or stowed manually by the vehicle operator.

A further benefit of the present apparatus is that in its undeployed orfolded state the apparatus is tightly folded against the rear of thevehicle and is folded in a manner that prevents inadvertent unfolding ordeployment. The apparatus unfolds into its deployed state or folds intoits undeployed state with little risk of fouling since the panels of theapparatus are hinged in a pre-determined relationship.

Yet another benefit is provided by the frame structure of the apparatusthat is easily mountable to the rear of a vehicle. The frame structureis configured to allow the stowed apparatus to assume as small anenvelop as possible to reduce its impact on opening the rear swing doorsof the truck. The frame structure is further configured to be easilymoved by hand to and from the stowed position, without the need fortools. Other benefits and objects of the drag-reducing apparatus can bediscerned from the following description along with the accompanyingfigures.

DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a drag reducing apparatus according toone embodiment, shown mounted on the rear of a vehicle in its initialundeployed state.

FIG. 2 is a perspective view of the drag reducing apparatus shown inFIG. 1 as the apparatus is moving from its undeployed state to itsdeployed state.

FIG. 3 is a perspective views of the drag reducing apparatus shown inFIG. 1 with the apparatus in its deployed state

FIG. 4 is a rear perspective view of the drag reducing apparatusdepicted in FIG. 1 shown in its initial undeployed state with one sidepanel section and a lower panel removed for clarity.

FIGS. 5-8 are perspective views of the drag reducing apparatus depictedin FIG. 4 illustrating the apparatus in sequential stages of movementfrom its undeployed state to its deployed state.

FIG. 9 is a rear perspective view of an alternative embodiment of thedrag reducing apparatus with one side panel section and a lower panelremoved for clarity.

FIG. 10 is a perspective view of a frusto-conical embodiment of the dragreducing apparatus, with the apparatus shown in its deployed state.

FIGS. 11-14 are perspective views of the drag reducing apparatusillustrated in FIG. 1 being moved to a stowed position clear of the reardoors of the trailer.

FIG. 15 is a top view of the drag reducing apparatus illustrated inFIGS. 11-14, shown with the apparatus in a stowed position with atrailer door opened at the rear of the trailer.

FIG. 16 is a top view of the drag reducing apparatus illustrated inFIGS. 11-14, shown with the apparatus in an alternative stowed position.

FIG. 17 is a perspective view of a modification to the drag reducingapparatus shown in the prior figures, with an additional interior panelshown in its stowed position.

FIG. 18 is a perspective view of another modification to the dragreducing apparatus shown in the prior figures, with additional interiorwings shown in their stowed position.

FIG. 19 is a perspective view of the drag reducing apparatus illustratedin FIG. 18, shown with the interior wings in their deployed position.

FIG. 20 is a rear perspective view of the mounting frame for a dragreduction apparatus according to a further embodiment.

FIG. 21 is a right rear perspective view of a drag reduction apparatusaccording to the further embodiment mounted on the rear of a trailer,with a portion of the apparatus removed for clarity.

FIG. 22 is a left rear perspective view of the drag reduction apparatusshown in FIG. 21, with a portion of the apparatus removed for clarity.

FIG. 23 is an enlarged perspective view of a portion of the mountingframe shown in FIG. 20.

FIGS. 24 a, 24 b are plan and side views, respectively, of an upperpanel section of the drag reduction apparatus shown in FIGS. 22-23.

FIGS. 25 a, 25 b are plan and side views, respectively, of a side panelsection of the drag reduction apparatus shown in FIGS. 22-23.

FIGS. 26 a, 26 b are plan and side views, respectively, of a lower panelsection of the drag reduction apparatus shown in FIGS. 22-23.

FIG. 27 is a perspective view of a hinge assembly of the mounting frameshown in FIGS. 20-22.

FIG. 28 is an enlarged perspective view of the interface between thehinge assembly of FIG. 27 and the mounting frame of FIG. 20.

FIG. 29 is a top view of the hinge assembly depicted in FIGS. 27-28,with the hinge assembly in the extended or open position relative to thetrailer.

FIG. 30 is an enlarged perspective view of a sealing element mounted tothe mounting frame of FIG. 20.

FIG. 31 is a side representation of the latch arrangement for engagingthe apparatus of the present embodiment to the trailer.

FIG. 32 is an enlarged perspective view of a latch assembly of the latcharrangement shown in FIG. 31.

FIG. 33 is a side view of the latch assembly shown in FIG. 32.

FIGS. 34 a-c are side views of the latch assembly shown in FIGS. 32-33,depicting stages of operation of the assembly.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Details of a drag reducing apparatus 10 are illustrated in FIGS. 1-2.The apparatus 10 can be self-deploying, meaning that the apparatusdeploys or extends automatically as the speed of the vehicle on which itmounted increases. Alternatively, the apparatus can be manually deployedand stowed. The apparatus simulates a truncated boat tail in itsdeployed position, shown in FIG. 2, thereby providing the vehicle withthe aerodynamic benefits associated with devices of this type. The dragreducing apparatus 10 is formed of an arrangement of lightweight panelshinged together so that the panels may assume a compact foldedconfiguration in its undeployed stated shown in FIG. 1. The apparatus isconfigured to automatically unfold and fold depending upon the speed ofthe vehicle and the air pressure experienced at the rear of the vehicle.

As shown in FIGS. 1-2, the apparatus 10 is mounted to the rear of atruck or trailer T, encircling the doors D of the vehicle. The doors Dmay be the double-door or “barn door” type depicted in the figure, orother forms of rear doors, such as a single hinged door or a roll updoor. When mounted to the vehicle, the apparatus essentially blocksaccess to the doors. Thus, in one aspect of the apparatus 10, theapparatus is capable of being moved to a stowed position clear of thedoors D to provide access for loading or unloading the truck T.

In one embodiment, the drag reducing apparatus includes an upper panelsection 12, a lower panel section 14, a left side panel section 16 and aright side panel section 18. In the undeployed state, shown in FIG. 1,the panel sections are folded over each other to sit close to the rearof the truck T. The panels are preferably formed of a lightweight yetresilient material, such as a polymer or composite material. The panelsmust be sufficiently rigid to hold their shape in the deployed stateshown in FIG. 2 without sagging or flexing. Moreover, the panels must besufficiently stiff to allow the apparatus to unfold automatically in themanner described herein. Thus, in a specific embodiment, the panels areformed of a fiber reinforced polypropylene or polyethylene, with athickness of about 0.06-0.13 inches.

The upper panel section 12 is formed of two panels 12 a and 12 b joinedby a center hinge 13 a, while the lower panel 14 section similarlyincludes two panels 14 a, 14 b joined by a center hinge 15 a. The twoupper panels 12 a, 12 b combine to form a slightly trapezoidal shape.Specifically, the combined length of the leading edge 12 c isapproximately equal to the width of the truck T, while the combinedlength of the trailing edge 12 d is slightly shorter. Thus, the sideedges of the panels 12 a, 12 b angle slightly inward from the leadingedge. The lower panels 14 a, 14 b also combine to form a more pronouncedtrapezoidal shape. The leading edge of the lower panels has a combinedlength equal to the combined length of the leading edge of the upperpanel section. However, the trailing edge 14 d is shorter than thetrailing edge 12 d so that the side edges 14 e are at a greater anglerelative to the leading edge of the lower panels. The difference intrapezoidal shapes of the upper and lower panel sections are a functionof the manner in which the apparatus 10 is configured to unfold, asexplained in more detail herein.

The left and right side panel sections 16, 18 are mirror images. Thus,the left side panel section 16 includes a center panel 16 a and anintermediate panel 16 b positioned between the center panel 16 a andupper panel 12 a. The intermediate panel 16 b is connected to the centerpanel 16 a by a hinge 16 b, while the intermediate panel is connected tothe upper panel 12 b by a hinge 13 b. The right side panel 18 is formedby a center panel 18 a connected by hinge 19 a to an intermediate panel18 b, which is then connected to the upper panel 12 a by a hinge 13 c.

The center panels 16 a, 18 a of the side panel sections 16, 18 are alsoconnected by hinges to the lower panel section 14. The lower panelsection 14 includes the aforementioned panels 14 a, 14 b, in addition tointermediate panels 14 c, 14 d, best seen in FIG. 2. The intermediatepanels 14 c, 14 d are connected by hinges 15 b and 15 c to acorresponding lower panel 14 a, 14 b. The intermediate panels 14 c, 14 dare also connected to a corresponding side center panel 16 a, 18 a byhinges 15 d, 15 e. It can be appreciated that the lower panel section 14provides a generally rectangular shape co-extensive with the upper panelsection 12. However, the lower panel section includes the two panels 14a, 14 b, as well as the two intermediate panels 14 c, 14 d that unfoldinto an essentially flat panel section in the deployed state shown inFIG. 2.

In the illustrated embodiment, each of the hinges 13 a-13 c, 15 a-15 e,17 a and 19 a are shown as traditional pintle-type hinge. However, othertypes of hinges are contemplated, including “living” hinges formed aspart of the panels themselves or hinges formed using high-strength tapespanning panel sections. The hinges should be capable of repeatedpivoting with only minimal resistance. Moreover, the hinges should becapable of a wide range of pivoting. For instance, as described in moredetail herein, all of the hinges pivot through at least about 90degrees, with the hinges 15 b, 15 c pivoting through almost 180 degrees.The center hinges also pivot through about 180 degrees, although thesehinges only play a role in stowing the apparatus, rather in its movementbetween undeployed and deployed states, as explained herein.

As shown in FIG. 1, in the undeployed state of the apparatus 10, thepanel sections are folded onto each other and most preferably are foldedso that the upper panel section 12 overlaps the side panel sections 16,18, which overlap the lower panel section 14. This configuration takesadvantage of the force of gravity to restore the panels from thedeployed state of FIGS. 2-3 to the undeployed or folded state of FIG. 1.The sequence of movements of the panel sections from undeployed todeployed states is shown in FIGS. 4-8.

In one embodiment, it is contemplated that the drag reducing apparatus10 may be self-deployed, meaning that the panels automatically unfold asthe truck T is traveling down the road. In particular, it is known thata region of low pressure trails the rear of a truck as it travels. Asthe speed increases, the pressure decreases, which coaxes the upperpanel section 12 to pivot upward, more or less in the manner that liftis generated over an airplane wing. As the upper panel section 12pivots, it pulls the intermediate panels 16 b and 18 b. As theintermediate panels move upward and pivot about the respective hinges 13b and 13 c, the intermediate panels pull the center panels 16 a and 18a, causing them to pivot outward. As the center panels pivot, they pullthe lower intermediate panels 14 c and 14 d, which in turn pull thelower panels 14 a and 14 b outward. The hinges constrain the panelsections 12, 14, 16 and 18 to move essentially in unison as the primarypanels 12 a/12 b, 14 a/14 b, 16 a and 18 a pivot outward, guided by thefour intermediate panels 16 b, 18 b, 14 c and 14 d. The sideintermediate panels 16 b, 18 b pivot and translate until they aregenerally co-planar with the corresponding side center panels 16 a, 18a. Likewise, the lower intermediate panels 14 c, 14 d pivot andtranslate until they are co-planar with the lower panels 14 a, 14 b, asshown in FIG. 8.

It is also contemplated that the apparatus 10 may be manually deployedby the truck operator prior to driving on the road. Once one of thepanels is manually displaced toward its deployed position, all of thepanels unfold in the same manner described above. Thus, in one approach,the operator can pull the lower panel section 14 downward, which will“transmit” this deployment movement first to the intermediate panels 14c, 14 d, then to the side panels 16, 18. As the side panels swingoutward from the truck doors D, this deployment movement is“transmitted” to the side intermediate panels 16 b, 18 b, which then inturn cause the upper panel section 12 to pivot upward to its deployedposition. This same deployment action can occur is one of the sidepanels 16, 18 is swung outward. The hinged connection between thevarious panels ensures that moving any large panel to its deployedposition will cause the other panels to become deployed.

The apparatus 10 remains in its deployed state of FIGS. 2-3 and 8 aslong as the air pressure behind the truck T is at a pre-determinedlevel. In a specific embodiment, the apparatus is calibrated to deploywhen the truck is traveling above about 35 m.p.h. When the truck slowsbelow this threshold speed, the pressure behind the truck is unable tokeep the panels “inflated”. Gravity works on the upper panel section 12causing it to begin to pivot downward. As the speed of the truckcontinues to drop, the upper panel section continues to pivot and theapparatus starts to fold back its deployed state. The sequence ofmovements of the panels essentially occurs in reverse sequence from thatdepicted in FIGS. 4-8. In order to assist in the folding movement, anelastic element 45, such as a bungee cord shown in FIG. 2, may beconnected between the fixed frame 20 and the lower panels 14 a, 14 b.The elastic elements can help overcome the effects of gravity thatattempt to hold the lower panels down during the folding steps. Theelastic elements may also help support the lower panels in theirdeployed state. In addition, or alternatively, the lower panel section14 may be lighter than the upper panel section 12 to thereby furtherbias the apparatus to be self-closing.

The apparatus 10 may always be manually deployed by the truck operatorbefore getting on the road. In certain embodiments, manual deployment isthe principal means for deployment in lieu of the automatic deploymentat a particular vehicle speed. In these embodiments, the panels can beconfigured to remain in their deployed configuration until manuallystowed by the operator. In certain specific versions, friction in thehinges may be sufficient to keep the apparatus deployed, even under theforces of vibration and shock from hitting chuckholes in the road. Inother versions, the hinges may incorporate a friction catch that holdsthe hinges in the deployed or stowed positions, or both. As a furthervariation, the panels and hinges can be configured so that the hingesmove past a “neutral” position in the deployed configuration so thatadditional force is necessary to move the hinge past this neutralposition to fold the panels.

In order to assist in the automatic deployment of the panels, the upperpanel section 12 may be configured to capture air flowing over the topof the truck T and direct the air beneath the panel section—i.e.,between the rear of the truck and the inner surface of the panels. Thus,as the truck speed increases, the airflow beneath the upper panelsection will increase to gradually push the upper panel section 12upward. This diverted airflow may pass through a gap defined between theleading edge 12 c of the upper panel section 12.

In an alternative embodiment, the drag reducing apparatus 10′ shown inFIG. 9 includes modified side and lower panel sections. In particular,these panel sections are modified so that all of the intermediate panelsare incorporated into the side panel sections. The upper and lower panelsections 12′ and 14′ are thus identically configured. The side panels,such as side panel 16′ shown in FIG. 9, includes a center panel 16 a′,an upper intermediate panel 16 b′ and a lower intermediate panel 16 c′,all joined by hinges 17 a′ and 17 b′.

In a further modification, the panels of the apparatus can be configuredso that the apparatus tapers slightly inward at all sides. Thus, in thedeployed state shown in FIG. 10, the apparatus 10″ is in afrusto-conical form. The intermediate panels 16 b″ and 16 c″ are at anangle to, and therefore not coplanar with, the upper, lower and sidecenter panels.

As explained above, the apparatuses 10, 10′ and 10″ are mounted to therear of the vehicle, and therefore block access to the rear doors. Thus,another feature of the apparatus 10 is incorporated into the manner inwhich the apparatus is mounted to an existing vehicle. In particular,the apparatus 10 is configured to move from its operating position shownin all of the figures thus far, to a stowed position, as shown in FIGS.11-14.

Referring first to FIGS. 1, 2 and 4, the apparatus 10 includes amounting frame 20 that is rectangular and generally corresponds to theperimeter of the rear of the truck while providing clearance fornecessary upper and lower lights for instance, as seen in FIG. 1. Themounting frame 20 includes a left frame section 22 and a right framesection 24 connected to each other by a center hinge 26. The panelsections are pivotably mounted to the frame sections by a series ofhinges, namely hinge array 34 for the upper panel section 12, hingearray 36 for the lower panel section 14, left side array 38 for the leftside panel section 16 and right side array 40 for the right side panelsection 18. The hinges can be the standard pintle-type hinges capable ofrepeated pivoting and able to withstand the elements on a movingvehicle, or may another hinge arrangement including the alternativehinges discussed above.

The mounting frame 20 includes elements for mounting the frame, andtherefore the entire apparatus 10, to the rear of a vehicle. Thus, theframe includes a left side mounting element 28 and a right side mountingelement 30 configured to fasten the corresponding frame sections 22, 24to the vehicle. In one embodiment, the mounting elements can be catchand latch arrangements on both sides of the frame. The entire apparatusis thus removed from the vehicle by releasing the catch and latcharrangement. However, it is preferred that the apparatus 10 remainmounted to the vehicle, rather than removed in its entirety. Thus, in apreferred embodiment, the left side mounting element is an array ofhinges 50, while the right side mounting element 30 may be an array oflatch components. The latch components can be a variety of types thatpreferably may be easily latched and unlatched, while providing a solidpositive engagement that can endure wind loads and vibrations associatedwith a truck traveling at highway speeds.

The latch components of the right side mounting element 30 areconfigured to be released to allow the entire apparatus 10—frame 20 andthe panel sections—to pivot to the side of the truck. Thus, as shown inFIG. 11, when the right side latches 30 are released, the right sideframe section 24 may be pivoted about center hinge 26. It should beapparent that the center hinges 13 a and 15 a at the upper and lowerpanel sections 12, 14 allow the panel sections to be folded over as theright frame section pivots. The right side frame section 24 is pivoteduntil it directly overlies the left side frame section 22, as shown inFIG. 12. The entire drag reducing apparatus 10 can then be pivoted aboutthe left side mounting hinges 28, as depicted in FIG. 13.

It can be noted in FIG. 14, that a latch 59 may be provided on the leftside of the truck T. The latch 59 may be configured like the right sidelatch 30 to engage a portion of the respective frame section 22, 24.

As further illustrated in FIG. 14 and in the overhead view of FIG. 15,the mounting frame 20 may be pivoted about the left side hinge array 28so that the left side frame section 22 is flush with the side of thetruck T. If the frame 20 simply pivots about the left side mountinghinges 28, the thickness of the folded apparatus 10 may impede theopening of the left side door D of the truck. Thus, the apparatus 10contemplates a feature that moves the folded frame away from the hingesH of the truck door D. In this embodiment, the left side hinge array 28includes extension hinges 50, as seen in FIGS. 14 and 15. The extensionhinge 50 includes a fixed hinge 52 that is mounted to the truck T and afixed plate 53 that is attached to the hinge 52. An extension plate 57is slidingly mounted over the fixed plate 53 so that the plate 57 can bepositioned adjacent the fixed hinge 52, as seen in FIG. 13, and thentranslated to the position shown in FIGS. 14-15 for stowing theapparatus 10. The extension plate 57 is attached to the frame 20 by ahinge 55, which allows the hinge assembly 50 to articulate in the mannernecessary to move the apparatus from the operative to the stowedpositions.

As shown in the overhead view of FIG. 15, the extension hinge 50 movesthe folded apparatus 10 away from the hinges H of the truck door D toallow the door to be pivoted close to the side of the truck T and wellclear of the rear of the truck. In the illustrated embodiment, the doorD can be pivoted to within 11 inches of the truck side. If the rightside frame section 24 is unfolded relative to the left section 22, asshown in FIG. 16, the stowed apparatus 10 sits flatter against the sideof the truck so that the truck door D can be pivoted even closer to thetruck. In the illustrated embodiment, the door D can be pivoted towithin 5.6 inches.

One benefit of the frame system of the apparatus 10 is that it permitsan intermediate storage position, and particularly the position shown inFIG. 12 in which the right side frame section 24 is folded onto the leftside frame section 22, but before the folded frame is pivoted to theside of the trailer T. Thus, in this intermediate storage configurationthe apparatus 10 is fully folded but remains situated at the rear of thetrailer. The two frame sections 22 and 24 can be held together by aseparate latch mechanism, by a bungee cord wrapped around the adjacentframe members, or by other suitable means for holding the sectionstogether. A cover mounted to the exposed frame section 24 may also beprovided to protect the panels from buffeting and from the elements.This intermediate storage position is particularly beneficial forintermodal applications in which a trailer box is carried by train orship. Stowing the apparatus 10 at the side of the trailer box puts it atrisk of damage as the containers are packed tightly next to each other.Moreover, the intermediate folded storage position of the apparatusreduces its exposure to the wind.

The intermediate storage position represented in FIG. 12 may also beused on the truck itself when the traveling speeds are not sufficient toobtain any aerodynamic benefit from the deployed apparatus. Thisalternative intermediate storage position keeps the apparatus at therear of the truck to avoid any increase in drag by disrupting the sideprofile of the vehicle.

The drag reducing apparatus 10 may be modified to incorporate aninterior deployable panel, such as the panel 70 shown in FIG. 17. Thispanel 70 is supported on the frame 20 by a hinge 72 mounted to a framemember 23 of one of the frame sections, such as the left side framesection 22. The panel is initially folded flat against one of the doorsD of the truck. After the drag reducing apparatus 10 is deployed, theinterior panel 70 is free to pivot to its deployed position shown inFIG. 17. In this position, the upper edge 74 of the panel supports thedeployed upper panel section 12 and the lower edge 76 rests against thelower panel section 14. In its deployed position, the panel 70 isaligned with the center hinges 13 a and 15 a of the respective panelsections. The panels and/or hinges may be configured to engage theinterior panel 70 in its deployed state to hold the panel in position.

The interior panel thus provides support for and adds rigidity to thedrag reducing apparatus. The interior panel 70 is particularlybeneficial to allow the panels forming the apparatus to be as thin aspossible. The interior panel helps maintain the apparatus in its dragreducing shape. It is contemplated in one embodiment that this interiorpanel 70 is provided with a apparatus 10 that is manually deployed. Theoperator thus deploys the apparatus 10 by moving one of the panels, asdescribed above. Once the apparatus is open, the operator can thenmanually pivot the interior panel 70 outward until it is aligned withthe center hinges 13 a, 15 a. Since the upper panel section 12 may dipslightly, some force may be required to pivot the interior panel fullyto its deployed position. In an alternative embodiment, the interiorpanel 70 may be configured with a center panel, a top panel and a bottompanel hingedly connected together. The top panel is hingedly connectedto one of the upper panels 12 while the bottom panel is connected to oneof the lower panels 14 so that when the upper and lower panel sections12, 14 deploy the interior panel is automatically deployed.

The embodiment shown in FIGS. 18-19 employs a similar concept, with theaddition of interior wings 80, 82. Each wing is pivotably mounted to acorresponding frame section, such as section 24, of the frame 20 by ahinge, such as hinge 84 shown in FIG. 18. The wings are hingedlyconnected to the frame 20 immediately adjacent the hinge arrays 38, 40for the side panels 16, 18, and may even be interleaved with those hingearrays. As shown in FIG. 18, the wings 80, 82 are sized to overlap intheir stowed configuration. The wings have a generally semi-circularshape with generally flat upper and lower edges 85, 86 to mate with theadjacent upper and lower panel sections 12, 14.

Like the interior panel 70 described above, the wings 80 and 82 remainedstowed flat against the doors of the truck until the apparatus 10 isfully deployed. The wings may then be pivoted about their respectivehinges until the wings 80, 82 are generally flush with the correspondingside panels 16, 18, as shown in FIG. 19. The semi-circular trailingedges 87 of the wings extend beyond the end of the panels in theapparatus 10 to increase the aerodynamic zone, or boat tailconfiguration, at the end of the truck. It can be appreciated that thewings 80, 82 provide an additional aerodynamic effect without having toincrease the length of the hinged panel apparatus 10.

In one modification, a flexible sheet 88 is fixed between the two wings80, 82. The sheet is formed of a thin but strong material, such asMylar, that can be easily folded relatively flat when the wings are intheir stowed position shown in FIG. 18. When the wings are deployed, thesheet 88 resembles a solid body appended to the rear of the vehicle toenhance the aerodynamic affect of the apparatus.

As shown in FIG. 19, when the wings 80, 82 are deployed, the side panels16 and 18 are somewhat redundant. In one embodiment, the wings may beattached to the side panels in their deployed states. In anotherembodiment, the extent of the side panels 16, 18 can be reduced to theminimal width necessary to connect the upper and lower panel sections inorder to retain the automatic folding and unfolding characteristic ofthe apparatus 10. In a further alternative, the side panels may beeliminated with appropriate modifications to the upper and lower panelsections 12, 14 and the wings 80, 82 to facilitate deployment andstorage.

When deployed on a tractor-trailer rig, the drag reduction apparatus 10significantly reduces drag, which has led to an increase in fuel economyand a commensurate decrease in fuel consumption. Computerized CFDanalysis reveal reductions in vortices that ordinarily form at the upperedge of the trailer, coupled with a “reduction” drag-generating negativepressure at the rear of the trailer. In the illustrated embodiment, thepanel sections 12, 14, 16 and 18 are configured to assume about a 15degree angle relative to the horizontal and vertical planes of thetrailer walls. The panel sections are approximately 30 inches in length.With this configuration, the CFD analysis predicts a reduction in totaldrag of about 8% from a standard trailer without the apparatus 10.

In this CFD analysis it was noted that a low pressure region is createdin the gap between the apparatus 10 and the rear of the trailer. In oneapproach, a sealing strip may be positioned within the gap. The stripmay be in the form of a rubber or elastomeric seal affixed to the rearperimeter of the frame 20. The seal compresses against the rear of thetrailer T when the apparatus 10 is mounted.

In an alternative approach, the gap is left open but the mounting frameis modified, such as the frame 120 of the alternative drag reducingapparatus 110 shown in FIGS. 20-22. The frame 120 is similar to theframe 20 described above with the inclusion of left and right sidemounting frame sections 122, 124 connected at their center beams 126 bya hinge element 127. The perimeter of the frame 120 is defined at eachframe section by a plurality of frame elements which include an upperextrusion or beam 135, a side extrusion or beam 137 and a lowerextrusion or beam 139, details of which are discussed below. Unlike themounting frame of the prior embodiments, the frame 120 includes upper,side and lower interior extrusions 140, 142 and 144, respectively, thatare offset from the perimeter frame extrusions, as shown in FIG. 20. Thespaces between the perimeter and the interior extrusions are spanned byupper, side and lower plates 130, 131 and 132, respectively. The centralportion of the frame 120 between the interior extrusions remains open.It has been found in CFD analysis that these interior panels offset orcancels the forces resulting from air flow through the gap between thetrailer T and the apparatus.

In a further feature of this embodiment, the panel sections areaugmented by tether sheets, as shown in FIGS. 21-22. As in the priorembodiment, the apparatus 110 includes upper, side and lower panelsections 180, 190 and 200 that fold and unfold in the same manner. InFIGS. 21-22 only the left side sections are shown, it being understoodthat the right side panel sections are similarly configured. The panelsections include an upper panel 182, side panels 192 and 194, and lowerpanels 201 and 202. The upper panel section 180 further includes anupper tether sheet 184 that is connected at its inboard edge to theupper interior extrusion 140 and at its outboard edge to the upper panel182. Likewise, the side panel section 190 includes a side tether sheet194 connected between the side panel 193 and the side interior extrusion142, while the lower panel section 200 includes a lower tether sheet 204connected to the lower panel 202 and the lower interior extrusion 144.

The tether sheets serve to control the outward or unfolded position ofthe panel sections. It is contemplated in one aspect that the tethersheets may be configured to achieve a pre-determined unfolded shape of acorresponding panel For instance, the side tether sheet 194 may beconfigured to introduce a slight vertical curvature to the side panel193. The panels are preferably formed of a flexible material that wouldallow their shape to be contoured using the restraint of the tethersheet.

An important objective of the tether sheets is to improve the dragreduction performance of the apparatus 110. In CFD analysis it has beenfound that introducing the tether sheets as depicted in FIGS. 21-22leads to an 11% reduction in aerodynamic drag from the bare trailer.This is in comparison to the 8% reduction achieved by the apparatus 10described above. In the analyzed embodiment, the panels are oriented atthe 15 degree angle described above. The tether sheets are also orientedat a 15 degree angle so that the tether sheets and associated panelstogether define a subtended angle of about 30 degrees.

A further benefit of the lower tether sheet 204 is that the slope of thesheet helps shed rain, snow and debris that may fall or be sucked intothe interior of the deployed apparatus 110. Thus, in one embodiment, thelower tether sheet is formed of a solid or close knit fabric material.The sheet may also be treated with a waterproofing composition. However,the upper sheet 184 and side tether sheet 194 need not be formed of thesame material. It has been found that forming these tether sheets of amesh material achieves substantially the same drag reduction benefit asa more solid material. The use of the mesh material in the upper andside locations means a lighter tether sheet that will not impede thefolding or unfolding of the apparatus 110.

As indicated above, the frame elements are in the form of extrusions. Asshown in FIG. 23, these extrusions define interlocking channels that areused for the connection of the panels and tether sheets to the frame.Thus, the upper extrusion 135 defines a interlocking channel 135 a, theside extrusion 137 a channel 137 a, and the lower extrusion 139 achannel 139 a. Likewise, the interior extrusions define correspondinginterlocking channels 140 a, 142 a and 144 a, as shown in FIGS. 21 and23.

The panel sections 180, 190 and 200 are configured to engage theinterlocking channels. Thus, as shown in FIGS. 24 a-b, the upper panelsection 180 includes an engagement rib 188 affixed to the interior edgeof the upper panel 182. The rib is sized to slide into one end of theinterlocking channel 135 a when the upper panel is installed. The uppertether sheet 184 includes a similar rib 189 that is configured to slideinto the channel 140 a. The interlocking channel and rib may beconfigured with a circular cross-section, a T-slot/T-bar configuration,or any other mating interface that allows the rib to be slid into anopen end of the channel and hold the end of the panel or sheet. As shownin FIGS. 25-26, the panels and tether sheets of the side and lower panelsections 190 and 200, include similar ribs 216, 218 (side panel) and210, 214 (lower panel) that engage the corresponding channels. It can benoted from FIGS. 25-26 that the triangular panels 192 and 202 do notrequire a rib because no edge of these panels engages an interlockingchannel.

It can thus be appreciated that the panels 182, 193 and 201 areconfigured to be removed and replaced independent of the other panels.This same independent replaceability is also incorporated into thetether sheets 184, 194 and 204. In order to fully capitalize on themodularity and ready removal/replacement of the panels, the dragreduction apparatus 110 incorporates additional features for theconnection of adjacent panels. In particular, referring first to FIG. 24a, the upper tether sheet 184 may be fastened by a tape strip 183 to theoutboard edge of the upper panel 182. The upper panel 182 furtherincludes a tape strip 186 extending alone an inboard side edge of thepanel. This tape strip 186 is fastened to the complementary right sideupper panel that forms the entire upper panel section 180 spanning thewidth of the apparatus frame 120. The tape strip 186 thus acts as ahinge at the joint between the two upper panels that allow the upperpanels to fold with the frame 120 when the apparatus 110 is to bepivoted clear of the trailer doors, as illustrated in FIG. 14, forinstance. The tape preferably incorporates sufficient rigidity so thatthe combined upper panels do not bow at the center joint. Thus, the tapestrip 186 may be a heavy duty vinyl tape.

The opposite side edge of the upper panel 182 interfaces with the uppertriangular panel 192 as seen in FIG. 22. To preserver the modularity ofthe panel construct, the upper panel 182 includes a removable fastenerstrip 185 at the edge adjacent the triangular panel 192. As shown inFIG. 25 a, the upper triangular panel 192 of the side panel section 190includes a mating removable fastener strip 198 extending from its freeupper edge. As seen in FIG. 21, the two mating strips 185, 198 areinitially separated but may be connected by overlaying the strip 198onto the strip 185. In one specific embodiment, this strip 185 mayincorporate a hook-and-loop fastener arrangement. However, othernon-permanent, easily removable fastener elements may be used that donot require a tool to remove, such as a zipper, snaps or othercomponents provided they are sufficiently strong to hold the panelstogether under high wind and vibration conditions experienced by theapparatus 110.

In FIG. 25 it can be seen that the side panel 191 includes a removablefastener strip 196 at its lower edge that is used to connect the sidepanel to the lower triangular panel 202 shown in FIG. 26. The lowertriangular panel 202 thus includes its own removable strip 208 so thatthe two strips 202 and 208 mate in the same way as the removable strips185, 198. In the illustrated embodiment, the upper triangular panel 192is fastened to the side panel 191 using a heavy duty tape strip 197.Similarly, the lower triangular panel 202 is fastened to the lower panel201 by a tape strip 206 and the left and right lower panels are attachedby a tape strip 207. It can be appreciated that full modularity can beachieved by replacing all of the tape strips with a removable fastenerstrip, such as the strips 196 and 208. In particular, the strips 186 and207 used to attach the left and right sides of the upper and lower panelsections may incorporate a removable fastener strip. However, it ispreferred that the tape strips be utilized at the joints between panelsthat are intended to reside in a mutual plane when the apparatus 110 isdeployed to avoid sagging or misalignment of a particular panel section180, 190, 200.

This modularity feature of the apparatus 110 extends to the hingearrangement that connects the apparatus to the body of the trailer T.Referring back to FIG. 20, the frame 120 includes a hinge assembly 150that includes a pair of hinge elements 151 a, 151 b connected to theframe 120 and a plurality of fixed hinges 153 that are fastened to thetrailer T, as shown in FIG. 22. The hinge elements 151 a, 151 b arepivotably connected to the fixed hinges 153 by a pivot rod 154 extendingthrough mating bores in the components. In one embodiment the fixedhinges 153 include a pivot plate 153 a that defines the bore to receivethe pivot rod 154, as shown in FIG. 28, and two right angle plates 153 band 153 c that are fastened directly to the body of the trailer usingconvention fasteners, such as screws or bolts. The right angle platesand particularly the plate 153 b are configured to rest flush againstthe side of the trailer. It can be appreciated that the fixed hinges 153offset the pivot point for the hinge elements 151 a, 151 b—i.e., thepivot rod 154—forward relative to the back of the trailer. This pivotpoint offset allows the frame 120 to be pivoted clear of the rear of thetrailer and close to the side of the trailer to avoid impeding theopening of the trailer door D, as can be seen in FIG. 29.

The fixed hinges may angle outward away from the trailer body to thepivot plate 153 a. As shown in FIG. 29, this configuration provides anaerodynamic shape to the fixed hinge. Moreover, this configurationensures that the fixed hinge 153 has a minimal profile that does notinterfere with trailer door D when the door is opened and pivoted on itsown hinges against the side of the trailer. An optional element is alsodepicted in FIG. 29, namely an extension plate 153 d that bridges thegap between the trailer body and the apparatus frame 120.

The manner in which the hinge assembly 150 engages the frame 120 isshown in FIGS. 27 and 28. In the illustrated embodiment, the hingeassembly includes two hinge plates 151 a and 151 b. To accommodatedifferent door hinge locations on the trailer, the hinge plate willtypically have different lengths—in FIG. 27 the hinge plate 151 b islonger than the hinge plate 151 a. The hinge assembly thus includeshinge spacer extrusions 160 a, 160 b and 160 c that interface with theside extrusion 137, as shown in FIG. 28. In one embodiment, the sideextrusion 137 includes an interlocking channel 165 that extends alongits entire length. The channel 165 is configured for a sliding fit withan interlocking element 164 on each hinge spacer extrusion 160. Eachhinge spacer extrusion defines a bore 161 through which a pivot rod 162extends. The pivot rod passes through the bore 161 in each of the hingespacer extrusions 160 a, 160 b, 160 c and an aligned bore in the hingeplates 151 a, 151 b. It can be appreciated that the hinge spacerextrusions may be sized as dictated by the trailer door hinge placementand by the optimal locations for attaching the fixed hinges 153 to thetrailer T. The upper and lower spacer extrusions may be provided with afastener bore 163 that can be used to fasten the spacer extrusion to theside extrusion 137 of the apparatus frame 120. Thus, the interlockingarrangement between the interlocking element 164 and channel 165,coupled with the fasteners through bores 163 ensure a solid engagementof the hinge assembly 150 to the frame. The same fastener can also trapthe pivot rod 162 within the bores 161.

The drag reduction apparatus 110 only requires one hinge assembly 150 oneither the right or left side of the frame 120. However, the same sideextrusion may be used on both the hinged and the non-hinged side. Thechannel 165 of the extrusion on the non-hinged side may be used to mounta sealing element 168, as shown in FIG. 30. The sealing element thusincludes a mating element 169 that slidably interlocks with the channel165 to permit easy installation or removal of the sealing element. Thesealing element is preferably sized to fill the gap between the trailerand the frame and may be formed of a flexible material, such as rubber.

The non-hinged side of the apparatus 110 includes components that fastenthe free end of the frame 120 to the trailer T. In one embodiment, thesecomponents include a latch plate 220 that is fastened to the trailer andextends downward at about a 45 degree angle. The latch plate isconfigured to be received in a latch receptacle 222 attached to theframe 120, as illustrated in FIG. 31. The receptacle preferably includesan angled lower surface 223 that is complementary with the latch plate220. When the frame is locked to the trailer, an upward movement of theframe moves the receptacle to the latch plate. As the angled platecontacts the angle surface 223 this contact draws the frame 120 closerto the trailer T.

As shown in FIG. 31, the second component for locking the apparatus tothe trailer includes a latch post 225 projecting outward from thetrailer. A latch assembly 230 is mounted to the frame 120 for engagingthe latch post and positively locking the frame to the trailer. Detailsof the latch assembly are shown in FIGS. 32-33. The latch assemblyincludes a base plate 232 that is attached to the back of the frame 120on the side opposite the hinge assembly 150 and in alignment with thelatch post 225. A handle 234 is pivotably mounted to the base 232 at apivot mount 238. This pivot point is close to the working end of thehandle that engages the latch post, namely the catch slot 236. Thegreater length of the handle is manipulated by the operator and providesa mechanical advantage when engaging the latch post with the latch slot.The latch slot 236 is contoured to draw the latch assembly 230 upward,which thereby draws the entire frame 120 upward. This movement moves thelatch receptacle 222 at the upper portion of the frame into engagementwith the latch plate 220, as described above.

The handle 234 is pivoted in one direction to engage the latch postwithin the latch slot and in the opposite direction to disengage. Thelatch assembly 230 includes a mechanism for locking the handle in theengaged configuration until deliberately released. Thus, the assemblyincludes a release lever 250 that defines a catch notch 252 adapted toengage a tang 254 projecting from the latch base plate 232. The tang 254includes a projection 254 a that serves as a stop for the handle 234 inits engaged position. As seen best in FIG. 33, the tang 254 is disposedwithin the catch notch 252 to lock the latch assembly in its engagedposition.

The release lever 250 is pivotably mounted to handle 234 at a pivotmount 262. The release lever includes a biasing arm 256 on the oppositeside of the pivot mount from the catch notch 252. This biasing armmaintains the release lever in the locked position until manuallyreleased by the operator. Thus, the biasing arm 256 bears against a rollpin 240 projecting from the handle 234. A biasing spring is connectedfrom the free end of the biasing arm 256 to a spring mount 260 on thehandle. The spring is calibrated to pull the release lever 252 againstthe roll pin 240, which thereby produces a moment at the catch notch 252to keep it in engagement with the tang 254. The biasing arm may bereleased by depressing the push pad 264 which pivots the release lever250 about the pivot mount 262, against the force of the spring 258, tofree the notch 252 from the tang 254. Once the release lever 250 hasbeen disengaged from the tang the handle is free to pivot in a directionto disengage the catch slot 236 from the latch post 225. This sequenceof operation is depicted in FIGS. 34 a-c.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected.

For instance, in the disclosed embodiments the folding panels aredescribed as mounted to a frame that is itself mounted to the vehicle.Alternatively, the folding panels may be mounted directly to the rear ofthe vehicle, such as to the rear door(s) of the vehicle. The panels ofdrag reducing apparatus in this alternative are configured to swing withthe door(s) of the vehicle.

1. A drag reducing apparatus for a vehicle, comprising: a frame having aperimeter and connectable to the rear of the vehicle; an upper panelsection, a lower panel section and opposite side panel sections, each ofsaid panel sections hingedly connected around said perimeter of saidframe, said upper panel section hingedly connected to an upper end ofeach of said side panel sections and said lower panel section hingedlyconnected to a lower end of each of said side panel sections, the hingedconnections between panel sections configured so that pivoting one ofsaid panel sections about a hinged connection automatically moves all ofthe panel sections from a folded state in which the panel sections aresubstantially flat against said frame to an extended state in which saidpanel sections project outward from said perimeter; and a series ofplates attached to said frame around said perimeter and disposed betweensaid panel sections in said folded state and the rear of the vehicle. 2.The drag reducing apparatus of claim 1, wherein said series of platesextend inwardly from said perimeter and are configured to define anopening therebetween.
 3. A drag reducing apparatus, comprising: a framehaving a perimeter and connectable to the rear of the vehicle; and anupper panel section, a lower panel section and opposite side panelsections, each of said panel sections hingedly connected around saidperimeter of said frame, said upper panel section hingedly connected toan upper end of each of said side panel sections and said lower panelsection hingedly connected to a lower end of each of said side panelsections, the hinged connections between panel sections configured sothat pivoting one of said panel sections about a hinged connectionautomatically moves all of the panel sections from a folded state inwhich the panel sections are substantially flat against said frame to anextended state in which said panel sections project outward from saidperimeter; wherein the hinged connection between each of said panelsections and said perimeter of said frame includes a slidinginterlocking interface.
 4. The drag reducing apparatus of claim 3,wherein said sliding interlocking interface includes: a plurality offrame elements forming said perimeter, each frame element defining aninterlocking slot; and a rib along one edge of each panel section, saidrib configured for sliding engagement and pivoting within saidinterlocking slot.
 5. The drag reducing apparatus of claim 4, whereinsaid interlocking slot includes a channel having a circularcross-section, and said rib has a complementary circular cross-section.6. The drag reducing apparatus of claim 3, wherein the hingedconnections between panel sections include a removable fastener stripfor removably connecting said panel sections.